The effectiveness of repetition as an aid to memory and learning depends on the spacing between repetitions. Repetition of events or information becomes increasingly beneficial with increases in the number of other events or items of information separating repetitions. There appear to be two distinguishable subphenomena in the effects of spaced repetition, depending on whether lags between repetitions are fairly short (1 to 5 items intervening) or longer. The subphenomena area referred to here as the "spacing effect" and the "lag effect," respectively. Developmental research by myself and others suggests that in free recall the spacing effect emerges between preschool and elementary school age whereas the lag effect seems to appear between elementary-school age and adulthood. Furthermore, developmental differences in spacing phenomena may depend on how memory is tested (e.g., recognition or free recall). Three studies are proposed here to identify and describe the developmental changes that do occur in spacing phenomena so that future research can be directed at the processes underlying these developmental effects and the effects of repetition and spaced repetition in general. In the first, subjects ranging from elementary-school age to young adulthood will be given a free recall task using word lists with both once-presented and repeated items distributed at various lags. The study is designed to determine specifically when the lag effect emerges and to verify that for at least some age groups spacing effects occur but lag effects do not. The second study further explores the emergence of the spacing effect, testing preschoolers and elementary school children for recognition of once-presented items and items repeated at various lags. The design of a third study depends on the outcome of the second. If in Study 2 preschoolers' performance indicates a spacing effect, it would then appear that retrieval conditions (e.g., recognition vs. recall) have an important influence on the spacing effect. Study 3a would explore further the retrieval conditions that may be necessary or sufficient to obtain a spacing effect with preschoolers. If no spacing effect is obtained with preschoolers in Study 2, Study 3b will explore some factors that may account for the lack of a spacing effect.